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Abstract:
The growth of laboratory reared Leuctra digitata Kempny was analysed by measuring labrum width from first to last larval instar in a series of exuviae of individual specimens. Mean labrum width increased at rates between 10 and 29 percent at moults and varied so much between successive moults of a single specimen and between specimens that adjacent means were never significantly different. An apparent pattern of varying growth rates may be laboratory induced. Overall mean increase of labrum width at moults was 17%. The growth of late instars of L. prima Kempny occured at constant mean 15% steps; adult head width was also 15% greater than last instar head width. In Nemurella pictetii Klapalek, increment steps were similar, 15 to 17%. The sexual size difference was also similar in every instar in all three species; apparently, the larger females underwent one moult more than males.
In Leuctra spp., external metamorphosis, i.e., essentially wing development, required 3 moults in the filed. The three wing-pad bearing larval instars have distinctive shapes, e.g., characteristic proportions of head width and wing length. The important weight gain and the maturation process during the last instar required several weeks. Mature specimens with dark wings emtied their guts. Since the gut contents usually included at least some sand, a distinct increase in the ash free portion of animal dry weight resulted.
In Nemurella pictetii, wing development was similar. Development of external male genitalia (paraprocts) at larval moults could be quantified; it also occured in 3 steps but modifications in the antepenultimate instar were not always distinct. Hence, instar discrimination based on paraprocts alone was less reliable than using wing-pads; only the combination permitted reliable instar recognition.
